Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.5.4.4 (adenosine deaminase)
 5,136 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Dextran-linked adenosine deaminase (EC 3.5.4.4) has been prepared. The polymer-linked enzyme possesses an optimal enzymatic activity of 27 units/mg immobilized protein (non-bound enzyme: 200 units/mg protein). Support-bound adenosine deaminase (4.5 microgram protein/mg dextran) shows an enhanced heat stability, a moderately increased Km, and a decreased V value compared to those of the free enzyme. The pH dependences of V and pKm values of dextran-linked adenosine deaminase show only two inflection points compared to three for the free enzyme, which are equivalent to the pK values of the enzyme. Since the missing third inflection point (pH 9.8) can be assigned to the pK value of the epsilon-amino group of lysyl residues, it can be concluded, that immobilization of adenosine deaminase on cyanogen-bromide-activated dextran took place via these lysyl residues. The remaining pK values found from the other inflection points are moderately shifted owing to the altered secondary structure. From the temperature dependence of the enzymatic activity, a 40% decrease of the activation energy of the support-bound enzyme was found, indicating diffusion controlled deamination. The immobilization of adenosine deaminase results in a fluorescence quenching of 80%, without shifting the ultraviolet maximum of the emission spectrum. As already shown for unmodified dextran, the matrix of polymer-linked adenosine deaminase is degradable by a bacterial endodextranase (EC 3.2.1.11).
 ...
PMID:Adenosine deaminase covalently linked to soluble dextran. The effect of immobilization on thermodynamic and kinetic parameters. 617 33

Dextran-bound adenosine, inosine, and nebularine have been prepared by carbodiimide coupling of their 2',3'-O-(4-carboxyethyl-1-methylbutylidene) cyclic acetal derivatives to 6-aminohexyldextran or 12-aminododecanyldextran. The latter polymers were prepared by cyanogen-bromide activation of dextran T80 followed by reaction with 1,6-diaminohexane or 1,12-diaminododecane. A high CNBr concentration leads to high-molecular-weight material, probably due to cross-linking, accompanied by a decrease in the digestion velocity using endo-dextranase from Penicillium species (EC 3.2.1.11). The dextran-bound nucleosides, as well as the nucleoside 2',3'-O-(4-ethoxycarbonyl-1-methylbutylidene) acetal derivatives, were tested as substrates and inhibitors for adenosine deaminase. The Km of the adenosine acetal ester is identical to that of adenosine which shows that acetalation does not hinder complex formation. Since the maximum velocity of deamination is decreased fourfold, the modified substrate does not fit as well as the nucleoside. The polymer-bound acetals show a 3-8-fold increase of Km or Ki and unchanged V compared to the corresponding acetals while dextranase digestion of the support does not alter the kinetic data. This indicates that the length of the polysaccharide chain does not interfere either with the complex formation or with the catalytic activity of the modified substrate. Since the activation energies of the deamination reactions of adenosine, its acetal ester, and dextran-linked adenosine are all similar (29.8-32.3 kJ mol-1) it is concluded that no diffusion control of the enzymatic reaction results from the binding of the nucleoside acetals to dextran T80.
 ...
PMID:Dextran-linked purine nucleosides as substrates and inhibitors of adenosine deaminase. 618 16

The use of polymers for delivering peptide and protein drugs is described. Soluble-polymer technology attempts to bind a polymer to all sites on therapeutic protein molecules that cause the body to recognize the molecules as foreign. Goals include a stable linkage, water solubility, low immunogenicity, prolonged half-life, and intact biological activity. Polyethylene glycol (PEG)-adenosine deaminase (ADA), or pegademase bovine, has FDA-approved labeling as replacement therapy for ADA deficiency in patients with severe combined immunodeficiency disease who are not suitable candidates for bone marrow transplantation. Pegademase bovine reverses the toxic accumulation of adenosine and deoxyadenosine in adenosine deaminase-deficient cells, restoring the immune system. PEG-asparaginase (pegaspargase) has shown promise in patients with acute lymphocytic leukemia; allergic reactions have been minimal. Animal studies suggest that superoxide dismutase has potential use in conditions in which the body's ability to remove oxygen free radicals is reduced, such as burns and myocardial infarction; coupling with PEG may greatly increase the protein's half-life. Other PEG-conjugated proteins under investigation include PEG-catalase, PEG-uricase, PEG-honeybee venom, PEG-hemoglobin, and PEG-modified ragweed pollen extract. Dextran, albumin, DL-amino acids, and polyvinyl pyrrolidone have also been studied as protein carriers; most of the products created thus far have not shown much promise. The coupling of polymers to proteins has yielded protein drugs with intact biological activity and reduced immunogenicity, but much remains to be learned about this technology.
 ...
PMID:Polymers for delivering peptides and proteins. 816 Jun 72